"I don't want my daughter seeing that," says Mrs. Gross of Sandy, her ninth grade daughter. "Now, I'm in a fight for the night over explaining to her why not."

Perhaps not anymore. Thanks to voluntary guidelines adopted by the National Association of Theatre Owners (NATO) - who operate 25,000 of the nation's 37,000 movie screens - scenes like this could become scarcer. In new measures agreed on last week, member operators agreed to stop showing movie previews for R-rated films at G- and PG-rated movies.

The agreement - which was one of 11 promises, that include extra staff to keep teens out of R-rated movies - are being seen as the latest action by the entertainment industry to address government concerns about the marketing of violent films to youths.

"We feel this is a very significant item in addressing what the Federal Trade Commission recommended in tightening up the movie industry's reaching out to audiences that are inappropriate," says John Fithian, association president.

After releasing a year-long study of industry advertising practices in September, the FTC blasted Hollywood for marketing its films inappropriately to youths. In congressional hearings and after visits to Hollywood by vice-presidential candidate Joseph Lieberman, some lawmakers suggested that such a system become law, enforceable by fines up to $10,000.

"We want to do as much as we can to be responsible with a voluntary system," says Mr. Fithian.

Many in the industry welcomed the move and said it would do much to alleviate public concerns raised by the FTC report.

"This is a positive measure that tries to ensure that children will not see what they are not supposed to see," says Bethlyn Hand, who leads a team that rates trailers for the Motion Picture Association of America. "This is just another step to help parents."

But others contend that such practices are already largely followed by several exhibitor chains. They say the new guidelines only serve as a formal nudge.

"Our policies have held for years that we are not to run trailers for R-rated movies to an audience watching G or PG-rated movies," says Brian Callaghan, spokesman for General Cinema Corp., which runs 700 screens in 20 states. "But this is encouraging us to redouble efforts and remind our theaters ... that we do take the issue very seriously."

Still other industry observers say the move is merely an election-year ploy to make it appear that practices have changed or will change.

"It will have little or no effect," says Robert Bucksbaum, editor of ReelSource, an industry newsletter. Most major theaters receive up to 300 films a year, some with trailers already attached, and he says it would be time-consuming and impractical for owners to police and respool all trailers to prevent such problems.

"Trailers come already attached to the film reels, and there is no way theater owners can pay attention to which audiences are watching them during which shows," says Mr. Bucksbaum, who also runs a theater of his own. "You might have one audience with children watching a film in the afternoon and another one with adults at night. It simply takes too long."

The new guidelines come on the heels of moves by the MPAA to curb controversial marketing practices. They also include prohibiting the screening of any trailers for films rated NC-17 before G, PG, or PG-13 films.

NATO companies also pledged to further monitor compliance policies with ID-checking policies adopted last year and to bring in extra staff for "extreme" R-rated films and for all NC-17 films. An "extreme" R-rated film, Mr. Callaghan says, might be "Scary Movie," or "South Park."

"We feel like this is a chance for us to reaffirm our policies and do a better job, but also remind the public that parents have to do their part," says Callaghan.